Fibrous formed products and methods for manufacturing such fibrous formed products

ABSTRACT

In a method of manufacturing a fibrous formed product, a mixture of fibers, including thick fibers and thin fibers, is prepared in order to form fibrous mats. The mixed fibers are supplied onto an outer peripheral surface of a roller. As the roller rotates, the mixed fibers are released from the roller and are thrown toward a fiber receiving surface. A fibrous mat is formed on the fiber receiving surface with a low-density layer next to the fiber receiving surface and a high-density layer on top of the low-density layer. Thick fibers mainly form the low-density layer and thin fibers mainly form the high-density layer. First and second fibrous mats are overlaid with one another such that their low-density layers oppose each other.

This application claims priority to Japanese patent application serialnumber 2003-142008, the contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to fibrous formed products that include alow-density layer coarsely formed mainly by thick fibers and interleavedbetween high-density layers that are closely formed mainly by thinfibers. The present invention also relates to methods of manufacturingsuch fibrous formed products.

2. Description of the Related Art

Japanese Laid-Open Patent Publication No. 6-200460 teaches a knownfibrous formed product and a method for manufacturing such a product.The known fibrous formed product of this publication is shown in FIG. 5and is labeled with reference letter “A”. The fibrous formed product “A”includes a low-density core layer 51, and upper and lower high-densitysurface layers, 53 and 55, disposed on the upper and lower surfaces ofthe core layer 51. The core layer 51 is coarsely formed mainly by thickinorganic fibers (15 μm in thickness). The surface layers 53 and 55 areclosely formed mainly by thin inorganic fibers (10 μm in thickness).

In order to manufacture the fibrous formed product “A”, differentmachines separately form the core layer 51, the upper surface layer 53,and the lower surface layer 55. These layers are then overlaid with oneanother and are needle-punched to form a fibrous mat. Subsequently, theupper and lower sides of the fibrous mat are overlaid with resin films.The resin films are heated. Finally, a heat press machine presses thefibrous mat with the heated resin films, bonding the fibers of the matto each other by the melted resin. Obtaining the fibrous formed product“A”.

However, the known method for manufacturing the fibrous formed product“A” requires several machines for separately forming the core layer 51and the upper and lower surface layers, 53 and 55. This may increase theoverall machine cost. In addition, because it is necessary to join thelayers 51, 53, and 55, after they are overlaid with one another, themanufacturing efficiency is relatively low.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to teach improvedtechniques that can reduce the machine cost for manufacturing fibrousformed products and that can increase the relative manufacturingefficiency of the fibrous formed products.

According to one aspect of the present teachings, methods ofmanufacturing fibrous formed products are taught. The fibrous formedproduct includes a low-density layer, coarsely formed mainly by thickfibers, interleaved between upper and lower high-density layers, closelyformed mainly by thin fibers. The methods may comprise the followingsteps (a) to (f):

-   (a) Preparing a mixture of fibers, including thick fibers and thin    fibers. The average weight of a thin fiber is less than the average    weight of a thick fiber.-   (b) Forming first and second fibrous mats from the mixed fibers.    Each of the first and second fibrous mats comprises a low-density    layer, coarsely formed mainly of thick fibers, and a high-density    layer, closely formed mainly of thin fibers. Each of the first and    second fibrous mat is formed by the following sub-steps (b1) and    (b2):    -   (b1) Supplying the mixed fibers onto the outer peripheral        surface of a roller. The roller configured so as to temporarily        retain the mixed fibers on the outer peripheral surface.    -   (b2) Rotating the roller so as to rotate the mixed fibers with        the roller and releasing the mixed fibers from the roller, so        that the mixed fibers are thrown toward a flat fiber-receiving        surface due to the rotational force of the roller. The released        fibers form a fibrous mat on the flat fiber-receiving surface.-   (c) Inverting one of the first and second fibrous mats.-   (d) Overlaying the first and second fibrous mats such that the    low-density layers of each fibrous mat oppose each other.-   (e) Joining the overlaid two fibrous mats to each other.-   (f) Bonding the fibers together.

According to these methods, the rotational force of the roller throwsthe mixed fibers from the outer peripheral surface of the roller,causing them to fall onto the flat fiber-receiving surface. Therefore,the thick fibers may reach the fiber-receiving surface before the thinfibers reach the fiber-receiving surface. Consequently, the low-densitylayer mainly comprising the thick fibers is formed first on the fiberreceiving surface. Thereafter the high-density layer, mainly comprisingthe thin fibers, is formed on the low-density layer via an intermediatelayer, referred to as a transition layer. As a result, a single processstep may form a fibrous mat on a fiber-receiving surface, the mat havinga low-density layer and a high-density layer.

The first fibrous mat and the second fibrous mat may be obtained by theabove step. One of the two mats is inverted. The two mats are thenoverlaid with each other such that the low-density layers directlyoppose each other. The first fibrous mat and the second fibrous mats arethereafter joined to each other. The fibers of the two mats are bondedtogether, forming a composite fibrous formed material having upper andlower high-density layers, and a low-density layer interleaved betweenthe high-density layers.

According to these methods, a fibrous mat having a low-density layer anda high-density layer can be formed with a single process step.Therefore, the number of machines required for manufacturing a fibrousformed product can be reduced in comparison with the known methods thatrequire separate machines for forming a low-density layer, an upperhigh-density layer, and a lower high-density layer. As a result, theoverall machine cost can be reduced. In addition, because the fibrousmat can be formed by a single process step, the fibrous matmanufacturing efficiency may be improved.

In another aspect of the present teachings, the same roller and the samefiber-receiving surface may be used to form the first and second fibrousmats.

In another aspect of the present teachings, different rollers may beused to form the first and second fibrous mats. In such a case, the step(c) may comprise positioning the first fibrous mat on a surface. Thefirst fibrous mat is oriented such that the high-density layer contactsthe surface and the low-density layer is exposed to the environment, forexample, in an upward orientation away from the surface. The secondfibrous mat is positioned such that the low-density layer of the secondfibrous mat is directly opposite the low-density layer of the firstfibrous mat. The second fibrous mat is placed upon the first fibrousmat.

Therefore, the second fibrous mat may be directly placed on the firstfibrous mat in order to form the fibrous formed product. Therefore, theefficiency of manufacturing the fibrous formed product can be furtherimproved.

In another aspect of the present teachings, the first and second fibrousmats are formed on different fiber-receiving surfaces. The step ofinverting the first fibrous mat (step (c)) also comprises automaticallyinverting and transferring the first fibrous mat onto a moving surfacelocated below the roller used for forming the second fibrous mat. Thesecond fibrous mat is formed directly upon the inverted first fibrousmat. The low-density layers of each mat are adjacent to one another.

In another aspect of the present teachings, the thin fibers compriseinorganic fibers and thermoplastic resin fibers. The thermoplastic resinfibers serve as agents for bonding the other fibers together. Morespecifically, the thermoplastic resin fibers may be melted by heat inorder to bond the inorganic fibers together and/or to bond the inorganicfibers to the thick fibers.

Preferably, the thermoplastic resin fibers comprise polypropylene fibershaving a diameter selected between 15 μm and 17 μm.

Preferably, the inorganic fibers comprise carbon fibers having adiameter less than

Preferably, the thick fibers comprise sisal hemp fibers having adiameter selected between 80 μm and 250 μm.

In another aspect of the present teachings, fibrous formed products aretaught that comprise a low-density layer coarsely formed mainly by thickfibers, and first and second high-density layers closely formed mainlyby the thin fibers. The low-density layer is interleaved between thefirst and second high-density layers. The thick fibers have a diameterselected between 80 μm and 250 μm. Preferably, the thick fibers comprisesisal hemp fibers.

Because the diameter of the thick fibers is equal to or larger than 80μm, the necessary thickness and rigidity of the fibrous formed productcan be ensured. However, because the diameter of the thick fibers isless than or equal to 250 μm, the low-density layer's ability to deformmay not be degraded, maintaining the formability of the fibrous formedproduct.

Preferably, the thin fibers comprise inorganic fibers and thermoplasticresin fibers. The thermoplastic resin fibers may serve as agents forbonding the other fibers together. For example, the thermoplastic resinfibers may be polypropylene fibers that have a diameter selected between15 μm and 17 μm.

Preferably, the inorganic fibers comprise carbon fibers that have adiameter of less than

In another aspect of the present teachings, fibrous mat manufacturingmachines are taught that include a rotary roller having an outerperipheral surface and a fiber retaining device for retaining fibers onthe outer peripheral surface within a predetermined angle of rotation. Asupplier serves to supply a mixture of thick fibers and thin fibers ontothe outer peripheral surface of the roller. A conveyor is disposed belowthe roller and is adapted to receive and convey the fibers that arethrown from the roller as the roller rotates. A fibrous mat is formed onthe conveyor comprising a high-density layer formed mainly by the thinfibers and a low-density layer formed mainly by the thin fibers.

Therefore, a fibrous mat having a high-density layer and a lower densitylayer can be manufactured by a single process step. As a result, thenumber of machines required for manufacturing the fibrous mat can bereduced. The one step process allows the manufacturing costs to bereduced and the manufacturing efficiency to be improved. Therefore, thesingle machine can be advantageously used in manufacturing a fibrousformed product having a low-density layer interleaved between a firstand second high-density layers.

Preferably, the fiber-retaining device comprises a plurality of needlesextending outward from the outer peripheral surface of the roller.

The fiber-retaining device may further include auxiliary rollers thatare disposed along the outer peripheral surface of the roller, and eachof the rollers is spaced from the outer peripheral surface of the rollerby a predetermined clearance.

Preferably, the conveyor comprises a conveyor belt that is driven at aconstant speed. The speed may be approximately proportional to theamount of material per length and/or the thickness of the resultingfibrous mat, for a given rotational speed of the roller.

In another aspect of the present teachings, fibrous mat manufacturingmachines are taught that may include a first and a second rotary roller.Each rotary roller has an outer peripheral surface. The outer peripheralsurface has a device for retaining fibers on the outer peripheralsurface within a predetermined angle of rotation. First and secondsuppliers respectively serve to provide a mixture of thick fibers andthin fibers onto the outer peripheral surfaces of the first roller andthe second roller. A first conveyor is disposed below the first rollerand serves to receive and convey the fibers. The fibers are thrown fromthe first roller as the first roller rotates, so that a first fibrousmat comprising a first high-density layer, formed mainly by the thinfibers, and a first low-density layer, formed mainly by the thickfibers, is formed on the first conveyor. A second conveyor is disposedbelow the first conveyor and the second roller. The second conveyorserves to receive and convey the first fibrous mat in an invertedposition. The second conveyor also serves to receive the fibers that arethrown from the second roller as the second roller rotates, so that asecond fibrous mat comprising a second high-density layer, formed mainlyby the thin fibers, and a second low-density layer, formed mainly by thethick-fibers, is formed on top of the first fibrous mat. The secondfibrous mat is formed such that the first low-density layer of the firstfibrous mat directly opposes the second low-density layer of the secondfibrous mat.

With this construction, the fibrous mat manufacturing machine cancontinuously manufacture a composite mat composed of the first andsecond fibrous mats. The composite mat has upper and lower, outerhigh-density layers, and an inner low-density layer interleaved betweenthe outer high-density layers. Therefore, the composite mat can bereadily used for example, in press forming manufacturing in order toproduce a product having a desired configuration, such as aconfiguration suitable for the ceiling material of an automobile.

Preferably, the fiber-retaining devices of the first and second rollerscomprise a plurality of needles extending outward from the outerperipheral surface of the corresponding roller.

Preferably, the fiber-retaining devices of the first and second rollersfurther include auxiliary rollers that are disposed along the outerperipheral surface of each of the corresponding rollers. Each of theauxiliary rollers is spaced apart from the outer peripheral surface ofeach of the corresponding rollers by a predetermined clearance.

Preferably, each of the first and second conveyors comprises a beltconveyor that is driven at a relatively constant speed.

Preferably, the first and second conveyors are driven in oppositedirections to one another. Therefore, the first fibrous mat may besmoothly inverted when the first fibrous mat is transferred onto thesecond conveyor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(A) is a schematic side view of a first representative fibrous matmanufacturing machine showing a first representative method formanufacturing a fibrous mat that is adapted to be formed into a fibrousformed product; and

FIG. 1(B) is a schematic vertical sectional view of the fibrous matabout the section BB; and

FIGS. 2(A) and 2(B) are schematic vertical sectionals views showing aninitial process for manufacturing the fibrous formed product byoverlaying first and second fibrous mats with one another; and

FIGS. 3(A) to 3(C) are schematic views showing a subsequent process formanufacturing the fibrous formed product; and

FIG. 3(D) is a schematic view showing a process for forming the ceilingmaterial for an automobile from the fibrous formed product; and

FIG. 4(A) is a schematic side view of a second representative fibrousmat manufacturing machine showing a second representative method formanufacturing a fibrous mat that is adapted to be formed into a fibrousformed product; and

FIGS. 4(B) and 4(C) are schematic vertical sectional views of a firstfibrous mat, taken about the section BB, and a composite mat, takenabout the section CC, formed by the second representative method; and

FIG. 5 is a schematic vertical sectional view of a known fibrous formedproduct.

DETAILED DESCRIPTION OF THE INVENTION

Each of the additional features and teachings disclosed above and belowmay be utilized separately or in conjunction with other features andteachings to provide improved methods and machines for manufacturingfibrous formed products, and the fibrous formed products manufactured bysuch methods and machines. Representative examples of the presentinvention, which examples utilize many of these additional features andteachings both separately and in conjunction with one another, will nowbe described in detail with reference to the attached drawings. Thisdetailed description is merely intended to teach a person of skill inthe art further details for practicing preferred aspects of the presentteachings and is not intended to limit the scope of the invention. Onlythe claims define the scope of the claimed invention. Therefore,combinations of features and steps disclosed in the following detaileddescription may not be necessary to practice the invention in thebroadest sense, and are instead taught merely to particularly describerepresentative examples of the invention. Moreover, various features ofthe representative examples and the dependent claims may be combined inways that are not specifically enumerated in order to provide additionaluseful embodiments of the present teachings.

(First Representative Embodiment)

A first representative fibrous formed product and a first representativemethod of manufacturing such a fibrous formed product will now bedescribed with reference to FIGS. 1 through 4. The first representativefibrous formed product is embodied as a panel that may be used as thebase material of a ceiling member in an automobile. FIG. 1(A) shows afirst representative machine 30 for manufacturing a fibrous mat. FIGS.2(A) and 2(B) show steps of manufacturing a fibrous mat that becomes thematerial of a fibrous formed product. FIGS. 3(A) through 3(D) show thesteps of manufacturing a ceiling member of an automobile.

Referring to FIG. 2(B), a fibrous formed product 10 is made of twosheets of fibrous mats 20. Each of the fibrous mats 20 are formed byapproximately 25% by weight of natural fibers, approximately 25% byweight of inorganic fibers, and approximately 50% by weight ofthermoplastic fibers. The natural fibers preferably may be sisal hempfibers having a thickness of about 150 to 160 μm and a length of about150 mm. The average weight of the sisal hemp fibers may be approximately0.082 g.

Th inorganic fibers preferably may be carbon fibers having a thickness(diameter) of about 7 μm and a length of about 100 mm. The averageweight of the carbon fibers may be approximately 0.0001 g.

The thermoplastic fibers are incorporated for bonding the inorganicfibers to each other and for bonding the inorganic fibers to the naturalfibers. Preferably, the thermoplastic fibers may be polypropylene fibersthat have a thickness (diameter) of about 15 to 17 μm and have a lengthof about 64 mm. The average weight of the polypropylene fibers may beapproximately 0.00002 g.

As shown in FIGS. 1(B), 2(A), and 2(B), a high-density layer 22 ispositioned on a top side (upper side) of each fibrous mat 20 and isclosely formed mainly by the thin and light fibers, such as the carbonfibers and the thermoplastic fibers. A low-density layer 24 ispositioned on the bottom side (lower side) of each fibrous mat 20 and iscoarsely formed mainly by the thick and heavy fibers, such as sisal hempfibers. The high-density layer 22 and the low-density layer 24 arejoined to each other via an intermediate layer 23. The intermediatelayer 23 does not define a distinct boundary but has a densitydistribution varying between the layers 22 and 24. In general for thisparticular embodiment, the percentage of the carbon fibers and thethermoplastic fibers in the intermediate layer 23 increases in thedirection toward the high-density layer 22. Conversely, the percentageof the sisal hemp fibers in the intermediate layer 23 increases in thedirection toward the low-density layer 24.

Two sheets of the fibrous mats 20 are used to form the fibrous formedproduct 10. The two sheets of fibrous mats 20 are overlaid with eachother such that the low-density layer 24 of one fibrous mat 20 directlyopposes the low-density layer 24 of the other fibrous mat 20 (as seen inFIGS. 2(A) and 2(B)). The fibrous mats 20 are then needle-punched by aneedle punching machine (not shown). The average surface density (massper unit area) of the fibrous mats 20 in the overlaid state ispreferably chosen to be approximately in the range of 450 g/m² to 600g/m².

The machine 30 for manufacturing the fibrous mats 20 will now bedescribed. The steps of manufacturing the fibrous formed product 10,formed of the fibrous mats 20, and the steps of manufacturing a ceilingmaterial, will be described after the machine 30 has been described. Theceiling material may be used for an automobile and may be formed fromthe fibrous formed product 10.

As shown in FIG. 1(A), the machine 30 for manufacturing the fibrous mats20 includes a main roller 32 that is rotatably driven while the sisalhemp fibers, carbon fibers, and thermoplastic fibers (hereinaftergenerally called “fibers F”) are temporarily carried or caught on anouter peripheral surface 34 of the main roller 32. To this end, the mainroller 32 has a horizontal rotational axis and a plurality of needles 36that extend outward from the outer peripheral surface 34 for carryingthe fibers F.

A plurality of auxiliary rollers 38 is disposed about the main roller 32and is arranged along a circumferential direction of the main roller 32along the outer peripheral surface 34. The auxiliary rollers 38 serve tohelp hold the fibers F carried on the outer peripheral surface 34 of themain roller 32. The auxiliary rollers 38 have rotational axes that areparallel to the rotational axis of the main roller 32. An outerperipheral surface 38 r of each auxiliary roller 38 is spaced apart fromthe outer peripheral surface 34 of the main roller 32 by a predetermineddistance. In addition, the auxiliary rollers 38 are rotatably driven ina direction opposite to the rotational direction of the roller 32, sothat the fibers F carried on the outer peripheral surface 34 of the mainroller 32 can smoothly pass through the spaces between the peripheralsurface 34 and the auxiliary rollers 38.

As indicated by an arrow in FIG. 1(A), the main roller 32 rotates in acounterclockwise direction and applies a rotational force (therotational force includes the centrifugal force and the inertial forceof the fibers F) to the fibers F. A fiber supplier 35 is disposed to theright and upper side of the main roller 32. The supplier 35 includes astorage tank 35 h and a supply device 35 f. The storage tank 35 h servesto store a substantially homogeneous mixture of the sisal hemp fibers,carbon fibers, and thermoplastic fibers. The supply device 35 f servesto supply the stored fibers F onto the outer peripheral surface 34 ofthe main roller 32 at a predetermined volume per unit of time.

A fiber conveyor 31 is configured as a conveyor belt and is horizontallydisposed below the main roller 32. The fiber conveyor 31 is driven so asto correspond to the rotation of the main roller 32. The fiber conveyor31 serves to receive the fibers F that have been thrown downward fromthe outer peripheral surface 34 of the main roller 32 by the rotationalforce of the main roller 32 (among other forces). The fiber conveyor 31is driven in a forward direction (right direction as viewed in FIG.1(A)) at a relatively constant speed. The result is that the fibers Fmay be piled up onto the fiber conveyor 31. The fibers F form a fiberlayer with a substantially uniform thickness. The driving speed of theconveyor 31 may be altered in order to adjust the thickness of the fiberlayer.

The step of manufacturing the fibrous mat 20 and the step ofmanufacturing the fibrous formed product 10 from two fibrous mats 20will be hereinafter be described in connection with the operation of themachine 30.

The main roller 32 is rotatably driven in a counterclockwise direction.The auxiliary rollers 38 are rotatably driven in a clockwise direction.The fiber conveyor 31 is driven so as to correspond to the rotation ofthe main roller 32. Once the main roller 32, the auxiliary rollers 38,and the conveyor 31, are all driven at their respective predeterminedspeeds, the fiber supplier 35 supplies fibers F onto the outerperipheral surface 34 of the main roller 32 at a predetermined volumeper unit of time.

The fibers F, supplied onto the outer peripheral surface 34 of the mainroller 32, are engaged and retained by the needles 36 and rotatesubstantially together with the main roller 32. Auxiliary rollers 38,disposed about and adjacent the outer surface 34 of the main roller 32,may hold the fibers F near the outer peripheral surface 34 of the mainroller 32. Therefore, the fibers F may be inhibited from being thrownout of connection with the main roller 32 by centrifugal force. When thefibers F, carried on the outer peripheral surface 34 of the main roller32, reach the lower side of the main roller 32, free of furtherauxiliary rollers 38, the fibers F may be thrown downward towards thefiber conveyor 31 by the rotational force (e.g., centrifugal force andthe inertia force) of the main roller 32.

As described previously, thick and heavy fibers (e.g. sisal hemp) andthe relatively thin and light fibers (e.g. carbon fibers andpolypropylene fibers) are mixed to form fibers F. The rotational forceof the main roller 32 acting upon the fibers F may allow the thick andheavy sisal hemp fibers to be thrown from the main roller 32 earlier andtherefore reach the fiber conveyor 31 prior to the thin and lightfibers, i.e. the carbon fibers and polypropylene fibers.

The result, as shown in FIG. 1(B), is that a coarse or low-density layer24, mainly comprising the thick and heavy sisal hemp fibers, may befirst formed on the conveyor 31. The close or high-density layer 22,mainly comprising the thin and light carbon fibers and polypropylenefibers, may be formed on top of the low-density layer 24. Thetransitional intermediate layer 23 is established at the boundary of thelow-density and high-density layers. The fibrous mat 20, having apredetermined thickness, may be formed on the conveyor 31 with thelow-density layer 24 positioned on the lower side (as seen in FIG.1(B)). Preferably, the speed of the conveyor 31 may be adjusted so thatthe fibrous mats 20 have an average surface density (mass per unit area)of approximately 450 g/m² to 600 g/m².

Two sheets of fibrous mats 20, manufactured by the machine 30 accordingto the above steps, are then overlaid with each other such that thelow-density layer 24 of one of the fibrous mats 20 directly opposes thelow-density layer 24 of the other of the fibrous mats 20, as shown inFIGS. 2(A) and 2(B). The overlaid fibrous mats 20 are then needlepunched by a needle punching machine (not shown), so that the fibrousmats 20 are joined to each other.

Thereafter, the punched fibrous mats 20 are heated to the meltingtemperature of the polypropylene fibers. As shown in FIG. 3(A), surfaceskin materials 26 are laid over the upper and lower surfaces of thebonded fibrous mats 20 through the intervention of adhesive films (notshown). A hot press machine 43 presses the bonded fibrous mats 20 alongwith the surface skin materials 26, as shown in FIGS. 3(A) and 3(B). Asa result, the melted polypropylene fibers may be impregnated throughoutthe carbon fibers of the high-density layer 22 and also throughout thesisal hemp fibers of the low-density layer 24. The carbon fibers arebonded to each other and are also bonded to the sisal hemp fibers. Inaddition, the surface skin materials 26 may be bonded to thecorresponding high-density layers 22 of the bonded fibrous mats 20 viathe melted polypropylene fibers and the adhesive films.

The pressure of the hot press machine 43 is then released as shown inFIG. 3(C). The bonded fibrous mats 20 with the surface skin materials 26bonded thereto are held in a released condition for a predetermined timeperiod in order to obtain the fibrous formed product 10. During thistime period, the thickness of the bonded fibrous mats 20 may recover tosome extent due to the restoration forces produced by the low-densitylayer 24. After the predetermined time period, the final steps formanufacturing the fibrous formed product 10 may be completed.

The fibrous formed product 10 may be transferred to a cold press machine45 for final shaping, as shown in FIG. 3(D). In this representativeembodiment, the fibrous formed product 10 is cold pressed to have aconfiguration for use as ceiling material of an automobile.

The ceiling material manufactured from the fibrous formed product 10preferably has an average surface density (mass per unit area) of about450 g/m² to 600 g/m². This representative embodiment may have athickness of approximately 3.5 to 4.5 mm. This thickness is greater thanthe typical thickness (e.g. about 3 mm) of a conventional fibrous formedproduct that may have the same average surface density as the fibrousformed product 10. However, the conventional fibrous formed product hasa uniform density throughout its thickness whereas the fibrous formedproduct 10 has layers of different densities.

According to the representative method of manufacturing the fibrousformed product 10, the fibrous mat 20, including the low-density layer24, intermediate layer 23, and the high-density layer 22, can bemanufactured through the use of a simple process and a single machine30. Overlaying two fibrous mats 20 such that their low-density layers 24oppose each other assembles the fibrous formed product 10. The number ofmachines of the representative method may be reduced, saving theassociated machine and other costs, in comparison with a conventionalmethod, where separate machines typically manufacture a core low-densitylayer, an upper high-density layer, and a lower high-density layer. Inaddition, because the fibrous mat 20, comprising a low-density layer 24,intermediate layer 23, and a high-density layer 22, is manufacturedduring a single process, there is an improvement in the manufacturingefficiency of the fibrous formed product 10 as compared to a typicalconventional method.

In addition, because sisal hemp fibers having a thickness (diameter)greater than or equal to 150 μm are used as the main material of thelow-density layer 24, the low-density layer 24 can provide the necessarythickness and the rigidity of the fibrous formed product 10. Inaddition, because the diameter of the chosen sisal hemp fibers is lessthan or equal to 160 μm, the low-density layer 24 may be relativelyeasily deformed, allowing the fibrous formed product 10 to be relativelyformable. However, the necessary thickness and the rigidity of thefibrous formed product 10 can still be maintained to some degree if thediameter of the sisal hemp fibers is greater than or equal to 80 μm. Inaddition, the fibrous formed product 10 may still be formable to acertain extent if the diameter of the sisal hemp fibers is chosen to beless than or equal to 250 μm.

Further, because the representative fibrous formed product 10 has alow-density layer 24 formed mainly by thick fibers, the fibrous formedproduct 10 may have a larger thickness than a conventional fibrousformed product with the same average surface density but with a uniformdensity throughout its thickness. Therefore, the clearance between themolds of the cold press machine 45 must be increased so that automobileceiling material, comprised of the representative fibrous formed product10 and formed by the cold press machine 45, may obtain a relativelylarger thickness.

Furthermore, because the thickness of the automobile ceiling materialcan be increased without affecting the average surface density, therigidity of the automobile ceiling material can be increased and theacoustic absorption property of the ceiling material can be improved.

(Second Representative Embodiment)

FIG. 4(A) is a schematic view of a second representative fibrous matmanufacturing machine 1 that can continuously form two fibrous mats 20so that they are automatically overlaid in the correct orientations withone another.

The machine 1 includes a first machine section 30 a, for manufacturingone of the two fibrous mats 20 (hereinafter called “first fibrous mat20”) and a second machine section 30 b, for manufacturing the other ofthe two fibrous mats (hereinafter called “second fibrous mat 20”). Thebasic construction of the first machine section 30 a and theconstruction of the second machine section 30 b are substantially thesame as with the first representative machine 30, described previously.Therefore, in FIG. 4(A), the parts of the first and second machinesections that are the same as parts of the first representative machine30 are labeled with the same reference numerals. A repeated descriptionof these parts will not be necessary.

The first machine section 30 a is different from the firstrepresentative machine 30 in that the roller 32 of the first machinesection 30 a is rotatably driven in the clockwise direction in order toapply a rotational force to the fibers F1. As a result, the supplier 35of the first machine section 30 a is positioned to the left and to theupper side of the roller 32.

The conveyor 31 is replaced with a first fiber conveyor 31 a(hereinafter also called “first conveyor 31 a”) and a second fiberconveyor 31 b (hereinafter also called “second conveyor 31 b”) that areconfigured as horizontal conveyor belts. The first and second conveyors31 a and 31 b are driven at their respectively predetermined relativelyconstant speeds.

The first conveyor 30 a is disposed below the roller 32 of the firstmachine section 30 a. Fibers Fl thrown down from the first machinesection's roller 32 may be received by the first conveyor 31 a so as toform a first fibrous mat 20. The first conveyor 31 a is driven to conveythe first fibrous mat 20 in a rearward direction (the leftward directionas viewed in FIG. 4(A)).

The second machine section 30 b is positioned forwardly (rightward asviewed in FIG. 4(A)) of the first machine section 30 a and has a mainroller 32 driven in the counterclockwise direction, applying arotational force to the fibers.

The second conveyor 30 b is positioned below the first conveyor 30 a andthe roller 32 of the second machine section 30 b. The second conveyor 30b may receive the first fibrous mat 20, transferred in an invertedorientation from the first conveyor 32 a. In addition the secondconveyor 30 b may receive fibers F₂ that are thrown downward from themain roller 32 of the second machine section 30 b. These fibers F₂ formthe second fibrous mat 20. The second fibrous mat 20 is formed on top ofthe first fibrous mat 20. The second conveyor 30 b conveys the combinedfirst and second fibrous mats 20 in the forward direction (to the rightas viewed in FIG. 4(A)).

In operation, the fibers F1 thrown downward from the main roller 32 ofthe first machine section 30 a and are received by the first conveyor 31a as described previously. Therefore, the first fibrous mat 20 may beformed on the first conveyor 31 a with the low-density layer 24positioned on the lower side. The first fibrous mat 20 may then beconveyed rearward (to the left as viewed in FIG. 4(A)). At the rear(left) end of the first conveyor 31 a, the first fibrous mat 20 may betransferred onto the second conveyor 31 b. Due in part to the conveyingdirection of the second conveyor 31 b being opposite to the conveyingdirection of the first conveyor 31 a, the first fibrous mat 20 may beinverted upside down when it is transferred to the second conveyor 30 b.

In other words, the first fibrous mat 20 may be transferred onto thesecond conveyor 31 b with the high-density layer 22 positioned on thelower side. This inverted first fibrous mat 20 is then conveyed forward(to the right as viewed in FIG. 4(A)) by the second conveyor 31 b. Thefirst fibrous mat 20 passes below the second machine section 30 b at arelatively constant speed. The fibers F₂ thrown downwardly from the mainroller 32 of the second machine section 30 b and are deposited onto thefirst fibrous mat 20 so as to have a substantially uniform thickness.Therefore, the second fibrous mat 20 is laid directly over the firstfibrous mat 20 with the low-density layer 24 of the second fibrous mat20 opposing the low-density layer 24 of the first fibrous mat 20.

The first and second fibrous mats 20 overlaid with each other at thelow-density layers 24 are then transferred to a needle punching machine(not shown) in order to be needle punched joined. The steps, necessaryto manufacture the fibrous formed product 10, following the needlepunching operation are the same as in the first representativeembodiment.

In this way, according to the second representative embodiment, thefirst and second fibrous mats 20 are continuously manufactured andautomatically overlaid with one another. The resulting manufacturingefficiency of fibrous formed product 10 may be further improved.

The present invention may not be limited to the above representativeembodiments but may be modified in various ways. Although sisal hempfibers are used as natural fibers forming the low-density layer 24 inthe above representative embodiments, any other natural fibers, such askenaf and palm fibers, among others, may be used in place of the sisalhemp fibers.

In addition, although carbon fibers are used as inorganic fibers thatform the high density layer 22, glass fibers and metal fibers, amongothers, may be used in place of carbon fibers.

Further, although polypropylene fibers are used as thermoplastic fibers,olefin resin fibers, such as polyethylene and polybutene fibers, amongothers, may be used in place of polypropylene fibers.

1. A method of manufacturing a fibrous formed product, wherein thefibrous formed product includes a low-density layer coarsely formedmainly by thick fibers interleaved between upper and lower high-densitylayers closely formed mainly by the thin fibers, comprising: (a)preparing a mixture of fibers including thick fibers and thin fibers,wherein an average weight of a thin fiber is smaller that an averageweight of a thick fiber; and (b) forming a first and second fibrous matfrom the mixed fibers, wherein each fibrous mat comprises a low-densitylayer coarsely formed mainly by the thick fibers and a high-densitylayer closely formed mainly by the thin fibers, and wherein each of thefibrous mats are formed by: (b1) supplying the mixed fibers onto anouter peripheral surface of a roller, wherein the roller is configuredso as to temporarily retain the mixed fibers on the outer peripheralsurface; and (b2) rotating the roller so as to rotate the mixed fiberswith the roller and releasing the mixed fibers from the roller, so thatthe mixed fibers are thrown toward a fiber receiving surface by arotational force of the roller so as to form a fibrous mat on the fiberreceiving surface; and (c) inverting the first fibrous mats; and (d)overlaying the inverted first fibrous mats with the second fibrous matssuch that the low-density layers of each fibrous mat oppose each other;and (e) joining the overlaid first and second fibrous mats to eachother; and (f) bonding the fibers together.
 2. The method as in claim 1,wherein the first and second fibrous mats are formed by utilizing thesame roller and the same fiber receiving surface.
 3. The method as inclaim 1, wherein different rollers form the first and second fibrousmats.
 4. The method as in claim 3, wherein the first and second fibrousmats are formed on different fiber receiving surfaces and wherein thestep (c) comprises: placing the first fibrous mat on a moving surfacelocated below the roller to be used in forming the second fibrous matsuch that the low-density layer of the first fibrous mat is positionedat the upper side of the first fibrous mat; and wherein the low-densitylayer, of the first fibrous mat placed on the moving surface locatedbelow the roller to be used in forming the second fibrous mat, becomesthe fiber receiving surface of the second fibrous mat; wherein the step(d) comprises; forming the second fibrous mat on top of the firstfibrous mat such that the low density layer of the second fibrous mat isformed opposed to the low-density layer of the first fibrous mat.
 5. Themethod as in claim 4, wherein the fiber receiving surface of the firstfibrous mat causes the first fibrous mat to move in an oppositedirection of the moving surface located below the roller to be used inthe forming of the second fibrous mat, and wherein the fiber receivingsurface of the first fibrous mat is positioned above the moving surfacelocated below the roller to be used in the forming of the second fibrousmat, and wherein the placing of the first fibrous mat of step (c)comprises having the first fibrous mat transfer from an end of the fiberreceiving surface of the first fibrous mat and land on the movingsurface located below the roller to be used in the forming of the secondfibrous mat, such that the low-density layer of the first fibrous mat ispositioned at the upper side of the first fibrous mat.
 6. The method asin claim 1, wherein the thin fibers comprise inorganic fibers andthermoplastic resin fibers, and the thermoplastic resin fibers serve asagents for bonding the other fibers together.
 7. The method as in claim6, wherein the thermoplastic resin fibers comprise polypropylene fibers.8. The method as in claim 7, wherein the polypropylene fibers have adiameter range between 15 μm and 17 μm.
 9. A method as in claim 6,wherein the inorganic fibers comprise carbon fibers.
 10. A method as inclaim 9, wherein the carbon fibers have a diameter less than 10 μm. 11.A method as in claim 1, wherein the thick fibers comprise sisal hempfibers.
 12. A method as in claim 11, wherein the sisal hemp fibers havea diameter selected between 80 μm and 250 μm.
 13. A fibrous formedproduct comprising: a low-density layer coarsely formed mainly by thickfibers; a first and second high-density layers closely formed mainly bythe thin fibers, wherein the low-density layer is interleaved betweenthe first and second high density layers; wherein: the thick fibers havea diameter selected between 80 μm and 250 μm.
 14. The fibrous formedproduct as in claim 13, wherein the thick fibers comprise sisal hempfibers.
 15. The fibrous formed product as in claim 13, wherein the thinfibers comprise inorganic fibers and thermoplastic resin fibers, and thethermoplastic resin fibers serve as agents for bonding the other fiberstogether.
 16. The fibrous formed product as in claim 15, wherein thethermoplastic resin fibers comprise polypropylene fibers.
 17. Thefibrous formed product as in claim 16, wherein the polypropylene fibershave a diameter selected between 15 μm and 17 μm.
 18. The fibrous formedproduct as in claim 15, wherein the inorganic fibers comprise carbonfibers.
 19. The fibrous formed product as in claim 18, wherein thecarbon fibers have a diameter less than 10 μm.
 20. The fibrous matmanufacturing machine, comprising: a rotary roller having an outerperipheral surface and a fiber retaining device for temporarilyretaining fibers on the outer peripheral surface; a supplier arrangedand constructed to supply a mixture of thick fibers and thin fibers ontothe outer peripheral surface of the roller; and a conveyor disposedbelow the roller and arranged and constructed to receive and convey thefibers that are thrown from the roller as the roller rotates, so that afibrous mat comprising a high-density layer, formed mainly by the thinfibers, and a low-density layer, formed mainly by the thin fibers, isformed on the conveyor.
 21. A machine as in claim 20, wherein the fiberretaining device comprises a plurality of needles extending outward fromthe outer peripheral surface of the roller.
 22. A machine as in claim21, wherein the fiber retaining device further includes auxiliaryrollers that are disposed adjacent the outer peripheral surface of theroller, and each of the auxiliary rollers is spaced apart from the outerperipheral surface of the roller by a predetermined clearance.
 23. Amachine as in claim 20, wherein the conveyor comprises a conveyor beltthat is driven at a constant speed.
 24. A fibrous mat manufacturingmachine, comprising: first and second rotary rollers each having anouter peripheral surface and a device for temporarily retaining fiberson the outer peripheral surface; and first and second suppliers arrangedand constructed to supply a mixture of thick fibers and thin fibers ontothe respective outer peripheral surfaces of the first roller and thesecond roller; a first conveyor disposed below the first roller andarranged and constructed to receive and convey the fibers that arethrown from the first roller as the first roller rotates, so that afirst fibrous mat comprising a first high-density layer formed mainly bythe thin fibers and a first low-density layer formed mainly by the thickfibers is formed on the first conveyor; a second conveyor, disposedbelow the first conveyor and the second roller, to receive and conveythe first fibrous mat in an inverted position and to receive the fibersthat are thrown from the second roller as the second roller rotates, sothat a second fibrous mat comprising a second high-density layer formedmainly by the thin fibers and a second low-density layer formed mainlyby the thick fibers is formed on the first fibrous mat such that thefirst low-density layer of the first fibrous mat opposes the secondlow-density layer of the second fibrous mat.
 25. A machine as in claim24, wherein the fiber retaining device comprises a plurality of needlesextending outward from the outer peripheral surface of the correspondingroller.
 26. A machine as in claim 25, wherein the fiber retaining devicefurther includes auxiliary rollers that are disposed adjacent the outerperipheral surface of the corresponding roller, and each of theauxiliary rollers is spaced apart from the outer peripheral surface ofthe corresponding roller by a predetermined clearance.
 27. A machine asin claim 24, wherein each of the first and second conveyors comprises aconveyor belt that is driven at a constant speed.
 28. A machine as inclaim 27, wherein the first and second conveyors are driven in opposingdirections to each other.